Inbred strains of mice are a powerful tool for modeling human biology and disease. Exploiting this potential, however, requires comprehensive phenotypic data on multiple inbred strains. The Mouse Phenome Project is an international collaborative effort headquartered at The Jackson Laboratory (TJL) to promote the phenotypic and genotypic characterization of a set of inbred strains and their derivatives for a broad range of traits relevant to human disease and to make the data publicly available. Since its inception in 1999, with support from TJL institutional funds, pharmaceutical corporations, and research foundations, the Mouse Phenome Project has collected a significant amount of phenotypic and genotypic data on as many as 40 inbred strains and created a public database for maintaining, dispersing, and analyzing these data (Mouse Phenome Database; MPD). These resources are increasingly important to the biomedical research community, as reflected in the heavy use of the MPD and significant research advances using MPD phenotypic and SNP data for the inbred strains. The Mouse Phenome Project is now poised for a major expansion and seeks funding to support ongoing and expanded functions. Major projects planned include further promoting and coordinating collaborative efforts to generate comprehensive phenotypic and genotypic data on inbred strains and their derivatives; continuing to populate the MPD with quality-controlled phenotypic and SNP data, and posting haplotype maps on the MPD; developing enhanced and new tools for retrieval and analysis of MPD data; and enhancing community access to integrated information on mouse genetics and biology by coordinating MPD efforts with those of the Mouse Genome Informatics group at TJL. Expansion of the Mouse Phenome Project will allow the biomedical research community to continue to exploit these resources together with emerging sequence, SNP, and haplotype data to uncover new information on the biological and genetic factors participating in normal biological and disease pathways.